Field of Invention
The present invention relates generally to apparatus and methods for electrical impedance control and synthesis, and more particularly to impedance control and synthesis by voltage.
Description of the Related Art
Electrical impedance is the measure of the opposition that a circuit presents to the passage of a current when a voltage is applied. In the prior arts, impedance is simulated using active analogue circuits in impedance synthesizers or emulators for a wide range of prescribed resistance, capacitance, and inductance values. As a major application, these impedance values are deployed as reference standards for calibrating electronic test and measurement instruments. During a calibration process, each of the reference components is individually measured by the instrument under calibration and the measured value is compared with the known value from which error of the instrument reading is determined. In general, different instruments may require different reference components. An impedance synthesizer can therefore provide conveniently a myriad of impedance values required for the calibration of many different instruments.
By the way the prior art impedance synthesizer is implemented there are however limitations in the power or voltage handling capabilities for the simulated components. Taking the following patents for example:
U.S. Pat. Nos. 4,963,845, 5,485,115, 5,585,741, 6,351,137, 6,369,650, 6,646,463, 7,808,314 and CN201141879, by which operational amplifiers, digital-to-analog converters, analog-to-digital converters and other linear active circuit elements are deployed in the impedance synthesizer circuits. The relatively low voltage and power handling capabilities of these semiconductor circuit elements have imposed limitations on the power or voltage handling capacities of the impedance synthesized thereof. This is fine for calibrating electronic test and measurement instruments as the impedance values at low signal levels are normally of interest in these applications.
In a different area of application the present invention is exploring however, electrical impedance synthesis techniques can be deployed to control electrical parameters other than instrument calibrations. For example, by varying the impedance of a load synthesized under a supply voltage, a controlled load current is formed. As another example, by controlling the impedance of a load synthesized by an impedance synthesizer and powering the same under at a supply voltage, the amount of power delivered to the load can be controlled. Further, through the control of impedance, and hence the control of current or power, other physical parameters such as temperature, luminosity, pressure, force, speed, etc. can be controlled. The idea, which appears still new to the academic and engineering communities, will be explained in the following specifications of the present invention.
For these applications where high power or high current is required, it would be very difficult and expensive if not impossible to deploy high power operational amplifiers and other active analog devices required for impedance synthesis in the traditional way, even if power efficiency is not taken into consideration.